1. Field of the Invention
The present invention generally relates, although not exclusively limited thereto, to a magnetic tape recording and/or reproducing apparatus such as, for example, a video tape recorder and, more particularly, to a reel braking mechanism employed in the video tape recorder for braking at least one of supply and take-up reels in order to avoid slackening of a length of magnetic recording tape that extends between two hubs within a magnetic tape cassette mounted in the video tape recorder.
2. Background Art
The video tape recorder capable of accommodating magnetic tape cassettes of different sizes selectively one at a time has been known in the art. By way of example, VHS-ready video tape cassettes now in the market are available in two types, standard and compact, which have different cassette sizes from each other. The standard video tape cassettes are rather prominently used in home video tape recorders which are coupled with television receiver sets and the compact video tape cassettes are mainly used in compact and portable video cameras. Regardless of the size of the cassette, both use magnetic recording tape which has the same tape width and are compatible with each other so far as information recording and reproducing schemes are concerned.
When it comes to recording or reproducing information on or from the magnetic recording tape within the compact video tape cassette through the home video tape recorder, a cassette adaptor of a size and shape both resembling those of the standard video tape cassette has been needed.
However, in order for the compact video tape cassette to be utilizable in the home video tape recorder without needing to use the cassette adaptor, a video tape recorder has been suggested in which when the compact video tape cassette is loaded in the video tape recorder, supply and take-up reels then spaced from each other a distance corresponding to the hub-to-hub distance of the standard video tape cassette can be driven to a position where the reel-to-reel distance attains a value corresponding to the hub-to-hub distance of the compact video tape cassette. An example of the suggested video tape recorder of the type having a capability of adjusting the reel-to-reel distance is shown in FIGS. 13 and 14.
In the video tape recorder of the known type shown in FIGS. 13 and 14, the supply and take-up reels are simultaneously movable between standard and compact cassette positions. The supply and take-up reels are movable along respective straight paths extending at an angle relative to each other so as to converge at a point away from the imaginary line connecting between respective axes of rotation of the supply and take-up reels. Since in this example the supply and take-up reels are rotatably supported in the same manner, reference will be made only to one of them, for example, the supply reel, and its associated parts.
Referring to FIGS. 13 and 14, a supply reel 110 is integrally formed with a reel spindle 110a and is engageable with any one of the hubs in any one of the standard and compact video tape cassettes. This supply reel 110 is rotatably mounted on a reel base 108 through a support shaft 109. Although not shown, the support shaft 109 is in turn drivingly coupled with a drive motor disposed beneath the reel base 108, either directly or through a drive transmission mechanism. The reel base 108 is movably mounted on a guide rail mechanism including two parallel guide rods 107 fixed at opposite ends thereof to a chassis of the video tape recorder and, therefore, the supply reel 110 is movable between the standard and compact cassette positions along the parallel guide rods 107.
In order to permit information to be recorded or reproduced on or from a length of magnetic recording tape in a stable fashion regardless of whether the tape cassette mounted is a standard video tape cassette or whether it is a compact video tape cassette, a reeled length of magnetic recording tape must be held still without being loosened within the video tape cassette when the video tape recorder is in an inoperative position (i.e., when actual information recording or reproduction is not called for when a reel drive mechanism is halted). To avoid the loosening of the reeled length of the magnetic recording tape, a reel braking mechanism has been employed.
The reel braking mechanism shown in FIGS. 13 and 14 comprises a solenoid unit 113 mounted on the reel base 108 and having a plunger, and a brake lever 112 having one end connected to the solenoid plunger and the other end provided with a brake pad 112a. A generally intermediate portion of the brake lever 112 is pivotally mounted on the reel base 108 through a support pin 111 so that when the solenoid unit 113 is electrically energized to retract the solenoid plunger, the brake lever 112 can be pivoted clockwise (or, counterclockwise so far as the tape-up reel, not shown, is concerned) about the support pin 111 with the brake pad 112a consequently separated away from the supply reel 110. However, since the brake lever 112 is biased counterclockwise about the support pin 111 by the action of a biasing spring 114 so long as the solenoid unit 113 is deenergized, the brake pad 112a is frictionally engaged with the supply reel 110 to prevent the length of magnetic recording tape within the tape cassette from being loosened.
According to the prior art shown in FIGS. 13 and 14, the solenoid unit is mounted on the corresponding reel base and is therefore movable together therewith. In other words, all component parts of the braking mechanisms associated respectively with the supply and take-up reels are mounted on the corresponding reel bases together with the associated reels and also together with the associated drive motors. Accordingly, the reel base for each of the supply and take-up reels must be of a size sufficient to accommodate not only the corresponding reel, but also the associated braking mechanism including the solenoid unit, the brake lever, the support pin and the biasing spring. Therefore, this requirement makes the video tape recorder as a whole bulky in size. Also, since the solenoid unit is mounted on the corresponding reel base, a space between the chassis and the bottom outer surface of the tape cassette when the reel spindles are engaged in the cassette hubs must be of a size to effectively avoid any possible contact between the mounted video tape cassette and top of the solenoid unit. That is, the space must be of a size corresponding to the sum of the height of the solenoid unit above the reel base and the clearance between the bottom of the solenoid unit and the chassis. This make it difficult to move the video tape recorder as a whole to have a compact size.
The video tape recorder of the type having the capability of adjusting the reel-to-reel distance such as discussed above is also disclosed in the Japanese Laid-open Patent Publication No. 5-151655, published Jun. 18, 1983, and the Japanese Laid-open Patent Publication No. 6-36395 published Feb. 10, 1994.
According to the Japanese Laid-open Patent Publication No. 5-151655, both of the supply and take-up reels are movable between the standard cassette position, in which the reel-to-reel distance corresponds to the hub-to-hub distance in the standard tape cassette, and the compact cassette position, in which the reel-to-reel distance corresponds to the hub-to-hub distance in the compact tape cassette, along a respective arcuate path about a support shaft through which an associated reel drive gear is rotatably mounted on a chassis. The braking mechanism employed in this known device includes a pivot lever employed for each of the supply and take-up reels, and is mounted on the chassis for pivotal movement between operative and inoperative positions. This pivot lever for each of the supply and take-up reels is provided with a brake pad frictionally engageable with the associated reel drive gear that is constantly meshed with a gear formed integrally with the corresponding reel. The reel drive gears are utilized to move the supply and take-up reels between the standard and compact cassette positions along the respective arcuate paths. The supply and take-up reels can be braked when the associated pivot levers are moved to the operative position with the corresponding brake pads consequently brought into frictional engagement with the reel drive gears. This prevents the length of magnetic recording tape within the tape cassette from being loosened regardless of whether the tape cassette mounted is a standard video tape cassette or whether it is a compact video tape cassette.
The braking mechanism disclosed in the Japanese Laid-open Patent Publication No. 5-151655 appears to be too complicated, because of the reel drive gear intervening between the brake lever and each of the supply and take-up reels. It, also, appears to be too complicated, because of the required sophisticated yet complicated mounts through which the supply and take-up reels can be supported on the chassis so as to revolve around the respective reel drive gears in meshed relation therewith.
On the other hand, the supply and take-up reels disclosed in the Japanese Laid-open Patent Publication No. 6-36395 are movable between the standard and compact cassette positions in a manner similar to those shown in and described with reference to FIGS. 13 and 14. The braking mechanism disclosed in this patent publication includes a trapezoidal brake plate mounted on a chassis for movement between engaged and disengaged positions, a biasing spring biasing the brake plate normally to the engaged position, and a brake pad secured to each of inclined edges of the brake plate for movement together therewith. A solenoid unit mounted on the chassis when energized during operation of the video tape recorder causes the brake plate, drivingly coupled therewith through a pivot lever, to move towards the disengaged position. However, when the solenoid unit is deenergized, the brake plate then held at the disengaged position is driven towards the engaged position by the biasing spring with the brake pads consequently brought into frictional engagement respectively with the supply and take-up reels. Each of the brake pads has a length sufficient to allow it to be frictionally engaged with the associated reel regardless of whether the supply and the take-up reels are held at the standard cassette position or whether they are held at the compact cassette position.
The braking mechanism disclosed in the Japanese Laid-open Patent Publication No. 6-36396 is advantageous in that the thickness of the video tape recorder as a whole can be reduced, that is, the video tape recorder can be compactly assembled, but has a problem in that the length of magnetic recording tape within the tape cassette cannot be smoothly braked to a halt.
Frictional engagements of the brake pads with the supply and take-up reels, respectively, take place simultaneously and under the same pressure when the brake plate is driven from the disengaged position to the engaged position by the action of the single biasing spring. However, the frictional force applied to the take-up reel from the corresponding brake pad acts in a direction of turn of the length of magnetic recording tape around the take-up reel relative to the direction of rotation of the take-up reel whereas the frictional force applied to the supply reel from the corresponding brake pad acts in a direction of departure of the length of magnetic recording tape from the supply reel relative to the direction of rotation of the supply reel. The braking force brought about by the frictional force acting in the direction of turn of the length of magnetic recording tape is higher than the braking force brought about by the frictional force acting in the direction of departure of the length of magnetic recording tape. Therefore, a difference occurs between the respective braking forces applied simultaneously to the supply and take-up reels. This difference in braking force does in turn bring about a difference between respective timings at which the supply and take-up reels are brought standstill even though the braking forces are simultaneously applied the supply and take-up reels, respectively. More specifically, due to the difference in braking force, the take-up reel can instantaneously braked to a halt, but the supply reel requires a substantial length of time before it is brought to a halt, resulting in loosening of the length of magnetic recording tape between the hubs within the tape cassette.
Also, since the single brake plate is used to apply braking forces to the supply and take-up reels, respectively, a problem has been found that one of the supply and take-up reels cannot be halted while the other of the supply and take-up reels is allowed to rotate.